1. Field of the invention
The present invention relates to a vehicle-mounted communication device which performs data communication using encrypted data with a roadside device disposed along a vehicular road. The present invention also relates to a cruising vehicle monitoring system which includes this vehicle-mounted device and the roadside device for monitoring vehicles that travel in the vicinity of the roadside device. In particular, the present invention relates to a device for performing automatic collection of a toll charge from a vehicle that travels along a toll road.
2. Description of Related Art
A toll charging system for automatically collecting a toll charge from a vehicle travelling along a toll road is well-known. This toll charging system includes a communication device (i.e., a roadside device) that is installed at an entrance or exit of the toll road and a communication device (i.e., a vehicle-mounted device) that is installed in a vehicle that travels along the toll road. This vehicle-mounted device transmits vehicle passenger data and method of payment data in response to an inquiry from the roadside device. This toll charging system performs automatic toll charge collection in the roadside device based on the transmission data from the vehicle-mounted device.
Meanwhile, in the above-mentioned system, because private information such as toll charge data, vehicle data, passenger data and the like are transmitted via radio communication between the vehicle-mounted device and the roadside device, there is a possibility that such data will be intercepted and wrongly used by a third party. For example, when a cash card is used for paying the toll charge, there is a possibility that cash card information will be intercepted and wrongly used.
Accordingly, in order to solve the above-mentioned problems, for example, one well-known proposal as disclosed in U.S. Pat. No. 5,310,999 proposes the execution of data communication between the vehicle-mounted device and the roadside device using encrypted data, which is obtained by encrypting the data to be transmitted, so that the contents of the data will be incomprehensible to the third party that intercepts such data.
Meanwhile, in the above-proposed system, because a known standardized encryption protocol such as the Data Encryption Standard (DES) algorithm for performing the reading and writing of data with respect to an IC card or the like is used for encrypting the communication data, the communication data between the vehicle-mounted device may be under certain circumstances decrypted relatively easily after such data is intercepted and analyzed. In this way, there may be problems regarding the confidentiality of data. Also, because it takes the DES algorithm a significant amount of time to perform the data encryption operation and because it is difficult to speed up this DES algorithm, the following problem occurs when the vehicle is moving fast and the DES algorithm is taking a significant amount of time in encrypting the transmission data and decrypting the reception data during communication operations between the vehicle-mounted device and the roadside device. That is, the vehicle-mounted device might leave a communication area of the roadside device before data communication operations are finished after the vehicle-mounted device enters the communication area of the roadside device.
For example, in the above-described toll charging system, when the vehicle-mounted device writes data (e.g., toll collection data) into a cash card or the like, and, after completion thereof, encrypts this data and transmits the encrypted data to the roadside device, the vehicle-mounted device first decrypts the data transmitted from the roadside device in order to perform the toll collection, then writes the data into the cash card or the like based on such decrypted data, encrypts the resulting data and transmits the encrypted result to the roadside device. However, it takes the foregoing system a significant amount of time to perform decryption of the data from the roadside device and encryption of the data to be transmitted to the roadside device. For example, assuming that the amount of time needed for the respective encryption and decryption operations is 30 ms and the cruising speed of the vehicle is 120 km/h, the vehicle travels one meter each time the vehicle-mounted device performs one encryption or decryption operation. On the other hand, since the communication area of the roadside device is set usually to a size that corresponds approximately to the size of the vehicle to prevent a plurality of vehicles from simultaneously entering into it, the travel distance of the vehicle within the communication area will be a few meters or so. Accordingly, in a highway where vehicles travel at speeds of approximately 120 km/h, because the encryption and the decryption operations need to be executed in both the vehicle-mounted device and the roadside device even during one-way communication to perform normal data communication between them, data communication (two-way communication) between the roadside device and the vehicle-mounted device can be performed once or twice at the most. If there are more communication operations, the vehicle-mounted device will go out of the communication area before communication operations are completed and thus, normal data communication becomes impossible.
On the other hand, in order to solve the above-mentioned problem, one may impose vehicle speed limits or replace an encryption device that performs the encryption operation in accordance with the DES algorithm with a device that enables high speed encryption processing. However, limiting the travel speed of the vehicle leads to traffic congestion and thus, negates the purpose of automatically collecting toll charges via radio communication, which is to lessen traffic congestion. Conversely, in order to make the processing speed of the encryption device faster, there is a need to use expensive encryption devices. Therefore, even if such expensive devices can be used for the roadside device, installation of such expensive encryption device in the vehicle-mounted device will be difficult to implement because this means increased burden on the toll road users.
Also, another option for increasing encryption speed is to use an encryption algorithm different from the DES algorithm, for example, an encryption algorithm that enables encryption to be performed through pipeline processing implemented using hardware. However, in this case, when the encryption device is constructed to perform encryption not through software processing using a CPU but via pipeline processing using special purpose hardware, the encryption device itself becomes expensive, and thus, even if it is possible to employ this construction for the roadside device, providing the same encryption device in the vehicle-mounted device will be difficult.